Methods and apparatus for multi-carrier communications with variable channel bandwidth

ABSTRACT

Methods and apparatus for multi-carrier communication with variable channel bandwidth are disclosed, where the time frame structure and the OFDM symbol structure are invariant and the frequency-domain signal structure is flexible. In one embodiment, a mobile station, upon entering a geographic area, uses a core-band to initiate communication and obtain essential information and subsequently switches to full operating bandwidth of the area for the remainder of the communication. If the mobile station operates in a wide range of bandwidths, the mobile station divides the full range into sub-ranges and adjusts its sampling frequency and its FFT size in each sub-range.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent. application Ser. No.10/583,534 (the '534 application) filed Jun. 5, 2007, now U.S. Pat. No.7,787,431. The '534 application is a National Stage Application andclaims the benefit of PCT Application No. PCT/US05/14828, filed on Apr.29, 2005 (the '828application). This application, as well as the '534application and the '828 application, claim the benefit of U.S.Provisional Patent Application No. 60/567,233, filed on May 1, 2004.This application also relates to PCT Application No. PCT/US2005/001939filed Jan. 20, 2005, which claims the benefit of U.S. ProvisionalApplication No. 60/540,032 filed Jan. 29, 2004; PCT Application No.PCT/US2005/004601 filed Feb. 14, 2005, which claims the benefit of U.S.Provisional Application No. 60/544,521 filed Feb. 13, 2004; PCTApplication No. PCT/US2005/003889 filed Feb. 7, 2005, which claims thebenefit of U.S. Provisional Application No. 60/542,317 filed Feb. 7,2004; and PCT Application No. PCT/US2005/008169 filed Mar. 9, 2005,which claims the benefit of U.S. Provisional Application No. 60/551,589filed Mar. 9, 2004.

BACKGROUND

While it is ideal fore broadband wireless communication device to beable to roam from one part of the world to another, wirelesscommunication spectra are heavily regulated and controlled by individualcountries or regional authorities. It also seems inevitable that eachcountry or region will have its own different spectral band forbroadband wireless communications. Furthermore, even within a country orregion, a wireless operator may own and operate on a broadband spectrumthat is different in frequency and bandwidth from other operators. Theexisting and future bandwidth variety presents a unique challenge indesigning a broadband wireless communication system and demandsflexibility and adaptability.

Multi-carrier communication systems are designed with a certain degreeof flexibility. In a multi-carrier communication system such asmulti-carrier code division multiple access (MC-CDMA) and orthogonalfrequency division multiple access (OFDMA), information is multiplexedon subcarriers that are mutually orthogonal in the frequency domain.Design flexibility is a result of the ability to manipulate parameterssuch as the number of subcarriers and the sampling frequency. Forexample, by using a different sampling frequency, a DVB-T (Digital VideoBroadcasting-Terrestrial) device is capable of receiving signalsbroadcasted from a DVB-T station that is operating on a 6-, 7-, or 8-MHzbandwidth.

However, the change in the time-domain structure brings about a seriesof system problems. A varying sampling rate alters the symbol length,frame structure, guard time, prefix, and other time-domain properties,which adversely affects the system behavior and performance. Forexample, the MAC layer and even the layers above have to keep track ofall the time-domain parameters in order to perform other networkfunctions such as handoff, and thereby the complexity of the system willexponentially increase. In addition, the change in symbol length causescontrol and signaling problems and the change in the frame structure maycause unacceptable jitters in some applications such as voice over IP. Apractical and feasible solution for multi-carrier communication withvariable channel bandwidth is desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic presentation of a radio resource divided intosmall units in both the frequency and time domains: subchannels and timeslots.

FIG. 2 illustrates a relationship between sampling frequency, channelbandwidth, and usable subcarriers.

FIG. 3 shows a basic structure of a multi-carrier signal in thefrequency domain, made up of subcarriers.

FIG. 4 shows a basic structure of a multi-carrier signal in the timedomain, generally made up of time frames, time slots, and OFDM symbols.

FIG. 5 shows a cellular wireless network comprised of a plurality ofcells, wherein in each of the cells coverage is provided by a basestation (BS).

FIG. 6 illustrates a variable channel bandwidth being realized byadjusting a number of usable subcarriers, whose spacing is set constant.

FIG. 7 depicts a time-domain windowing function applied to OFDM symbolsto shape the OFDM spectrum to conform to a given spectral mask.

FIG. 8 depicts a preamble designed to occupy either an entire operatingbandwidth or a core-band.

FIG. 9 shows an entire range (e.g., from 5 Mhz to 40 MHz) of bandwidthvariation being divided into smaller groups or trunks (e.g., 5-10 MHz,10-20 MHz, 20-40 MHz, in sizes), wherein each trunk is handled in oneparticular range.

FIG. 10 illustrates a multi-cell, multi-user cellular system comprisingmultiple base stations and mobile stations.

DETAILED DESCRIPTION

The multi-carrier system mentioned here can be of any format such asOFDM, or Multi-Carrier Code Division Multiple Access (MC-CDMA). Thepresented methods can also be applied to downlink, uplink, or both,where the duplexing technique is either Time Division Duplexing (TDD) orFrequency Division Duplexing (FDD).

The following description provides specific details for a thoroughunderstanding of the various embodiments and for the enablement of oneskilled in the art. However, one skilled in the art will understand thatthe invention may be practiced without such details. In some instances,well-known structures and functions have not been shown or described indetail to avoid unnecessarily obscuring the description of theembodiments.

The terminology used in the description presented below is intended tobe interpreted in its broadest reasonable manner, even though it isbeing used in conjunction with a detailed description of certainspecific embodiments of the invention. Certain terms may even beemphasized below; however, any terminology intended to be interpreted inany restricted manner will be overtly and specifically defined as suchin this Detailed Description section.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” Words using the singular or pluralnumber in this Detailed Description section also include the plural orsingular number respectively. Additionally, the words “herein,” “above,”“below” and words of similar import, when used in this application,shall refer to this application as a whole and not to any particularportions of this application. When the claims use the word “or” inreference to a list of two or more items, that word covers all of thefollowing interpretations of the word: any of the items in the list, allof the items in the list and any combination of the items in the list.

Multi-Carrier Communication System

The physical media resource (e.g., radio or cable) in a multi-carriercommunication system can be divided in both the frequency and timedomains. This canonical division provides a high flexibility and finegranularity for resource sharing. FIG. 1 presents a radio resourcedivided into small units in both the frequency and timedomains—subchannels and time slots. The subchannels are formed bysubcarriers.

The basic structure of a multi-carrier signal in the frequency domain ismade up of subcarriers. Fora given bandwidth of a spectral band orchannel (B_(ch)) the number of usable subcarriers is finite and limited,whose value depends on a size of an FFT (Fast Fourier Transform)employed, a sampling frequency (f_(s)), and an effective bandwidth(B_(eff)). FIG. 2 illustrates a schematic relationship between thesampling frequency, the channel bandwidth, and the usable subcarriers.As shown, the B_(eff) is a percentage of B_(ch).

A basic structure of a multi-carrier signal in the frequency domain ismade up of subcarriers and, illustrated in FIG. 3, which shows threetypes of subcarriers as follow:

-   -   1. Data subcarriers, which carry information data;    -   2. Pilot subcarriers, whose phases and amplitudes are        predetermined and made known to all receivers, and which are        used for assisting system functions such as estimation of system        parameters; and    -   3. Silent subcarriers, which have no energy and are used as        guard bands and DC carriers.

The data subcarriers can be arranged into groups called subchannels tosupport scalability and multiple-access. Each subchannel may be set at adifferent power level. The subcarriers forming one subchannel may or maynot be adjacent to each other. Each user may use some or all of thesubchannels. A subchannel formed by the contiguous subcarriers is calleda congregated or clustered subchannel. A congregated subchannel may havea different power level from others.

FIG. 4 illustrates the basic structure of a multi-carrier signal in thetime domain which is generally made up of time frames, time slots, andOFDM symbols. A frame consists of a number of time slots, whereas eachtime slot is comprised of one or more OFDM symbols. The OFDM time domainwaveform is generated by applying the inverse-fast-Fourier-transform(IFFT) to the OFDM signals in the frequency domain. A copy of the lastportion of the time waveform, known as the cyclic prefix (CP), isinserted at the beginning of the waveform itself to form an OFDM symbol.

The downlink transmission in each frame begins with a downlink preamble,which can be the first or more of the OFDM symbols in the first downlink(DL) slot. The DL preamble is used at a base station to broadcast radionetwork information such as synchronization and cell identification.

Similarly, uplink transmission can begin with an uplink preamble, whichcan be the first or more of the OFDM symbols in the first uplink (UL)slot. The UL preamble is used by mobile stations to carry out thefunctions such as initial ranging during power up and handoff, periodicranging and bandwidth request, channel sounding to assist downlinkscheduling or advanced antenna technologies, and other radio functions.

Cellular Wireless Networks

In a cellular wireless network, the geographical region to be servicedby the network is normally divided into smaller areas called cells. Ineach cell the coverage is provided by a base station. This type ofstructure is normally referred to as the cellular structure. FIG. 5depicts a cellular wireless network comprised of a plurality of cells.In each of these cells the coverage is provided by a base station (BS).

A base station is connected to the backbone of the network via adedicated link and also provides radio links to the mobile stationswithin its coverage. Within each coverage area, there are located mobilestations to be used as an interface between the users and the network. Abase station also serves as a focal point to distribute information toand collect information from its mobile stations by radio signals. If acell is divided into sectors, from system engineering point of view eachsector can be considered as a cell. In this context, the terms “cell”and “sector” are interchangeable.

Variable Bandwidth OFDMA

In accordance with aspects of certain embodiments of the invention, avariable bandwidth system is provided, while the time-domain signalstructure (such as the OFDM symbol length and frame duration) is fixedregardless of the bandwidths. This is achieved by keeping the ratioconstant between the sampling frequency and the length of FFT/IFFT.Equivalently, the spacing between adjacent subcarriers is fixed.

In some embodiments, the variable channel bandwidth is realized byadjusting the number of usable subcarriers. In the frequency domain, theentire channel is aggregated by subchannels. (The structure of asubchannel is designed in a certain way to meet the requirements of FEC(Forward Error Correction) coding and, therefore, should be maintainedunchanged.) However, the number of subchannels can be adjusted to scalethe channel in accordance with the given bandwidth. In such realization,a specific number of subchannels, and hence the number of usablesubcarriers, constitute a channel of certain bandwidth.

For example, FIG. 6 illustrates the signal structure in the frequencydomain for a communication system with parameters specified in Table 1below. The numbers of usable subcarriers are determined based on theassumption that the effective bandwidth B_(eff) is 90% of the channelbandwidth B_(ch). The variable channel bandwidth is realized byadjusting the number of usable subcarriers, whose spacing is setconstant. The width of a core-band is less than the smallest channelbandwidth in which the system is to operate.

TABLE 1 Sample System Parameters Sampling freq. 11.52 MHz FFT size 1024points Subcarrier spacing 11.25 kHz Channel bandwidth 10 MHz 8 MHz 6 MHz5 MHz # of usable subcarriers 800 640 480 400

In this realization, using the invariant OFDM symbol structure allowsthe use of same design parameters for signal manipulation in thetime-domain for a variable bandwidth. For example, in an embodimentdepicted in FIG. 7, a particular windowing design shapes the spectrum toconform to a given spectral mask and is independent of the operatingbandwidth.

Radio Operation Via Core-Band

To facilitate the user terminals to operate in a variable bandwidth (VB)environment, specific signaling and control methods are required. Radiocontrol and operation signaling is realized through the use of acore-band (CB). A core-band, substantially centered at the operatingcenter frequency, is defined as a frequency segment that is not greaterthan the smallest operating channel bandwidth among all the possiblespectral bands that the receiver is designed to operate with. Forexample, for a system that is intended to work at 5-, 6-, 8-, and10-Mhz, the width of the CB can be 4 MHz, as shown in FIG. 6. The restof the bandwidth is called sideband (SB).

In one embodiment relevant or essential radio control signals such aspreambles, ranging signals, bandwidth request, and/or bandwidthallocation are transmitted within the CB. In addition to the essentialcontrol channels, a set of data channels and their related dedicatedcontrol channels are placed within the CB to maintain basic radiooperation. Such a basic operation, for example, constitutes the primarystate of operation. When entering into the network, a mobile stationstarts with the primary state and transits to the normal full-bandwidthoperation to include the sidebands for additional data and radio controlchannels.

In another embodiment, a preamble, called an essential, or primarypreamble (EP), is designed to only occupy the CB, as depicted in FIG. 8.The EP alone is sufficient for the basic radio operation. The EP can beeither a direct sequence in the time domain with its frequency responseconfined within the CB, or an OFDM symbol corresponding to a particularpattern in the frequency domain within the CB. In either case, an EPsequence may possess some or all of the following properties:

-   -   1. Its autocorrelation exhibits a relatively large ratio between        the correlation peak and sidelobe levels.    -   2. Its cross-correlation coefficient with another EP sequence is        significantly small with respect to the power of the EP        sequences.    -   3. Its peak-to-average ratio is relatively small.    -   4. The number of EP sequences that exhibit the above three        properties is relatively large.

In yet another embodiment, a preamble, called an auxiliary preamble(AP), which occupies the SB, is combined with the EP to form afull-bandwidth preamble (FP) (e.g., appended in the frequency domain orsuperimposed in the time domain). An FP sequence may possess some or allof the following properties:

-   -   1. Its autocorrelation exhibits a relatively large ratio between        the correlation peak and sidelobe levels.    -   2. Its cross-correlation coefficient with another FP sequences        is significantly small with respect to the power of the FP        sequences.    -   3. Its peak-to-average ratio is relatively small.    -   4. The number of FP sequences that exhibits the above three        properties is relatively large.

In still another embodiment, the formation of an FP by adding an APallows a base station to broadcast the FP, and a mobile station to useits corresponding EP, to access this base station. An FP sequence mayalso possess some or all of the following properties:

-   -   1. Its correlation with its own EP exhibits a relatively large        ratio between the correlation peak and sidelobe levels.    -   2. Its cross-correlation coefficient with any EP sequence other        than its own is significantly small with respect to its power.    -   3. The number of FP sequences that exhibit the above two        properties is relatively large.        Automatic Bandwidth Recognition

The VB-OFDMA receiver is capable of automatically recognizing theoperating bandwidth when it enters in an operating environment orservice area of a particular frequency and channel bandwidth. Thebandwidth information can be disseminated in a variety of forms toenable Automatic Bandwidth Recognition (ABR).

In one embodiment, a mobile station, when entering in an environment oran area that supports the VB operation or services, will scan thespectral bands of different center frequencies. If it detects thepresence of a signal in a spectral band of a particular center frequencyby using envelope detection, received signal strength indicator (RSSI),or by other detection methods, it can determine the operating channelbandwidth by bandwidth-center frequency association such as tablelookup. For example, a table such as Table 2 is stored in the receiver.Based on the center frequency that it has detected, the mobile stationlooks up the value of the channel bandwidth from the table.

TABLE 2 Sample Center Frequency and Corresponding Bandwidth Centerfrequency Channel Bandwidth 2.31 GHz 10 MHz 2.56 GHz  6 MHz  2.9 G  8MHz

In another embodiment, the system provides the bandwidth information viadownlink signaling, such as using a broadcasting channel or a preamble.When entering into a VB network, the mobile stations will scan thespectral bands of different center frequencies in which the receiver isdesigned to operate and decode the bandwidth information contained inthe broadcasting channel or preamble.

Multi-Mode (Multi-Range) VB-OFDMA

In accordance with the principles of this invention, multi-modes aredevised for a VB-OFDMA system to handle an exceptionally wide range ofvariation in channel bandwidth. The entire range of bandwidth variationis divided into smaller parts—not necessarily in equal size—each ofwhich will be dealt with as a separate mode or range.

FIG. 9 illustrates the entire range (e.g., from 5 MHz to 40 MHz) ofbandwidth variation being divided into smaller parts (e.g., 5-10 MHz,10-20 MHz, 20-40 MHz, in sizes). Each part is handled in one particularmode. The mode for the lowest range of bandwidth is labeled as“fundamental mode” and other modes are called “higher modes” (Mode 1,Mode 2, etc.).

The sampling frequency of a higher mode is higher than the samplingfrequency of the fundamental mode. In one embodiment the samplingfrequency of a higher mode is a multiple of the sampling frequency ofthe fundamental mode. In this embodiment, in the higher modes, the FFTsize can be multiplied in accordance with the sampling frequency,thereby maintaining the time duration of the OFDM symbol structure. Forexample, the parameters for the case of a multi-mode design are given inTable 3. Alternatively, a higher mode can be realized by maintaining theFFT size and shortening the OFDM symbol duration accordingly. Forexample, for Mode 1 in Table 3, the FFT size can be maintained at 1024,whereas the sampling frequency is doubled and the symbol length is ahalf of that for the fundamental range. Yet another higher-moderealization is to both increase the FFT size and shorten the symbolduration accordingly. For example, for Mode 2 (20 MHz to 40 MHz inbandwidth), both the FFT size and the sampling frequency can be doubledas those of the fundamental range, whereas the symbol length is halvedas that of the fundamental range. The width of the CB in a multi-modeVB-OFDMA system may not be greater than the smallest bandwidth in thefundamental mode.

TABLE 3 Sample System Parameters Mode 1 Fundamental-Mode Sampling freq23.04 MHz 11.52 MHz FFT size 2048 points 1024 points Subcarrier 11.25kHz spacing Channel 20 18 15 12 10 8 6 5 bandwidth (MHz) # of usable1600 1440 1200 960 800 680 480 400 subcarriers

FIG. 10 illustrates a multi-cell, multi-user cellular system comprisingmultiple base stations and mobile stations. The system of FIG. 10 is anexample of an environment in which the attributes of the invention canbe utilized.

While specific circuitry may be employed to implement the aboveembodiments, aspects of the invention can be implemented in a suitablecomputing environment. Although not required, aspects of the inventionmay be implemented as computer-executable instructions, such as routinesexecuted by a general-purpose computer, e.g., a server computer,wireless device or personal computer. Those skilled in the relevant artwill appreciate that aspects of the invention can be practiced withother communications, data processing, or computer systemconfigurations, including: Internet appliances, hand-held devices(including personal digital assistants (PDAs)), wearable computers, allmanner of cellular or mobile phones, multi-processor systems,microprocessor-based or programmable consumer electronics, set-topboxes, network PCs, mini-computers, mainframe computers, and the like.Indeed, the term “computer” refers to any of the above devices andsystems, as well as any data processor.

Aspects of the invention can be embodied in a special purpose computeror data processor that is specifically programmed, configured, orconstructed to perform one or more of the processes explained in detailherein. Aspects of the invention can also be practiced in distributedcomputing environments where tasks or modules are performed by remoteprocessing devices, which are linked through a communications network,such as a Local Area Network (LAN), Wide Area Network (WAN), or theInternet. In a distributed computing environment, program modules may belocated in both local and remote memory storage devices.

Aspects or the invention may be stored or distributed oncomputer-readable media, including magnetically or optically readablecomputer discs, hard-wired or preprogrammed chips (e.g., EEPROMsemiconductor chips), nanotechnology memory, biological memory, or otherdata storage media. Indeed, computer implemented instructions, datastructures, screen displays, and other data under aspects of theinvention may be distributed over the Internet or over other networks(including wireless networks), on a propagated signal on a propagationmedium (e.g., an electromagnetic wave(s), a sound wave, etc.) over aperiod of time, or they may be provided on any analog or digital network(packet switched, circuit switched, or other scheme). Those skilled inthe relevant art will recognize that portions of the invention reside ona server computer, while corresponding portions reside on a clientcomputer such as a mobile or portable device, and thus, while certainhardware platforms are described herein, aspects of the invention areequally applicable to nodes on a network.

The above detailed description of the embodiments of the invention isnot intended to be exhaustive or to limit the invention to the preciseform disclosed above. While specific embodiments of, and examples for,the invention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whileprocesses are presented in a given order, alternative embodiments mayperform routines having steps in a different order, and some processesmay be deleted, moved, added, subdivided, combined, and/or modified.Each of these processes may be implemented in a variety of differentways.

The teachings provided herein can be applied to other systems, notnecessarily the system described herein. The elements and acts of thevarious embodiments described above can be combined to provide furtherembodiments. Aspects of the invention can be modified, if necessary, toemploy the systems, functions, and concepts of the various referencesdescribed above to provide yet further embodiments of the invention.

Particular terminology used when describing certain features or aspectsof the invention should not be taken to imply that the terminology isbeing redefined herein to be restricted to any specific characteristics,features, or aspects of the invention with which that terminology isassociated. In general, the terms used in the following claims shouldnot be construed to limit the invention to the specific embodimentsdisclosed in the specification, unless the above Detailed Descriptionsection explicitly defines such terms. Accordingly, the actual scope ofthe invention encompasses not only the disclosed embodiments, but alsoall equivalent ways of practicing or implementing the invention.

The above detailed description of the embodiments of the invention isnot intended to be exhaustive or to limit the invention to the preciseform disclosed above or to the particular field of usage mentioned inthis disclosure. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. Also, the teachingsof the invention provided herein can be applied to other systems, notnecessarily the system described above. The elements and acts of thevarious embodiments described above can be combined to provide furtherembodiments.

Aspects of the invention can be modified, if necessary, to employ thesystems, functions, and concepts of the various references describedabove to provide yet further embodiments of the invention.

Changes can be made to the invention in light of the above “DetailedDescription.” While the above description details certain embodiments ofthe invention and describes the best mode contemplated, no matter howdetailed the above appears in text, the invention can be practiced inmany ways. Therefore, implementation details may vary considerably whilestill being encompassed by the invention disclosed herein. As notedabove, particular terminology used when describing certain features oraspects of the invention should not be taken to imply that theterminology is being redefined herein to be restricted to any specificcharacteristics, features, or aspects of the invention with which thatterminology is associated.

In general, the terms used in the following claims should not beconstrued to limit the invention to the specific embodiments disclosedin the specification, unless the above Detailed Description sectionexplicitly defines such terms. Accordingly, the actual scope of theinvention encompasses not only the disclosed embodiments, but also allequivalent ways of practicing or implementing the invention under theclaims.

While certain aspects of the invention are presented below in certainclaim forms, the inventors contemplate the various aspects of theinvention in any number of claim forms. Accordingly, the inventorsreserve the right to add additional claims after filing the applicationto pursue such additional claim forms for other aspects of theinvention.

We claim:
 1. A cellular base station, comprising: circuitry configuredto transmit a broadcast channel in an orthogonal frequency divisionmultiple access (OFDMA) core-band, wherein the core-band issubstantially centered at an operating center frequency and thecore-band includes a first plurality of subcarrier groups, wherein eachsubcarrier group includes a plurality of subcarriers, the core-banddefined as a frequency segment with a bandwidth that is not greater thana smallest operating channel bandwidth among a plurality of operatingchannel bandwidths, the core-band having a same value for the pluralityof operating channel bandwidths, wherein the circuitry is furtherconfigured to maintain a fixed spacing between adjacent subcarriers andto adjust a number of usable subcarriers to realize a variable band,wherein the number of usable subcarriers is determined based on theplurality of operating channel bandwidths; and circuitry configured totransmit control and data channels using the variable band including asecond plurality of subcarrier groups, wherein the variable bandincludes at least the core-band.
 2. The cellular base station of claim1, wherein the circuitry configured to transmit the broadcast channel isfurther configured to transmit radio network information in thebroadcast channel.
 3. The cellular base station of claim 1, furthercomprising circuitry configured to transmit synchronization informationin the core-band.
 4. The cellular base station of claim 1, wherein thecircuitry configured to transmit the broadcast channel is furtherconfigured to transmit in a time slot format.
 5. The cellular basestation of claim 1, wherein the base station operates in an OFDMAfrequency division duplex (FDD) or time division duplex (TDD) mode.
 6. Avariable bandwidth communication method, comprising: receivingsynchronization information by a cellular mobile station from a basestation in an orthogonal frequency division multiple access (OFDMA)core-band, wherein the core-band is substantially centered at anoperating center frequency and the core-band includes a first pluralityof subcarrier groups where each subcarrier group includes a plurality ofsubcarriers having a fixed spacing between adjacent subcarriers, whereina number of usable subcarriers is adjustable to realize a variable band,wherein the number of usable subcarriers is determined based on aplurality of operating channel bandwidths, the core-band defined as afrequency segment with a bandwidth that is not greater than a smallestoperating channel bandwidth among the plurality of operating channelbandwidths, the core-band having a same value for the plurality ofoperating channel bandwidths, wherein the cellular mobile station isconfigured to operate within the plurality of operating channelbandwidths; synchronizing the cellular mobile station with the basestation using the received synchronization information; and receivingcontrol and data channels by the cellular mobile station using thevariable band including a second plurality of subcarrier groups, whereinthe variable band includes at least the core-band.
 7. The method ofclaim 6, wherein the receiving of the synchronization information by thecellular mobile station from the base station in the core-band includesreceiving cell identification information from the base station in thecore-band.
 8. The method of claim 6, further comprising receiving by thecellular mobile station a broadcast channel in the core-band.
 9. Themethod of claim 8, wherein the broadcast channel carries radio networkinformation.
 10. The method of claim 6, further comprising transmittingby the cellular mobile station a preamble after synchronizing with thebase station.
 11. A mobile station, comprising: circuitry configured toreceive broadcast information to access an orthogonal frequency divisionmultiple access (OFDMA) system, wherein the broadcast information isreceived only in a first band having a first bandwidth and the broadcastinformation is carried by a plurality of groups of subcarriers with eachgroup having a plurality of contiguous subcarriers; and circuitryconfigured to determine a second bandwidth of a second band that isassociated with the OFDMA system based upon the broadcast informationreceived in the first band, wherein a second bandwidth of the secondband is greater than the first bandwidth of the first band, wherein thefirst band is contained within the second band, wherein a data channelis carried by at least one subcarrier group of the second band, whereinthe plurality of contiguous subcarriers have fixed spacing, wherein anumber of usable subcarriers is adjustable to realize a variable band,wherein the number of usable subcarriers is determined based on aplurality of operating channel bandwidths, and wherein the first band isdefined as a frequency segment with a bandwidth that is not greater thana smallest operating channel bandwidth among the plurality of operatingchannel bandwidths, the first band having a same value for the pluralityof operating channel bandwidths wherein the mobile station is configuredto operate within the plurality of operating channel bandwidths.
 12. Themobile station of claim 11, further comprising circuitry configured toreceive a preamble that carries information on sector identity or cellidentity.
 13. The mobile station of claim 11, further comprisingcircuitry configured to receive information about the second band toenable the mobile station to receive the data channel.
 14. The mobilestation of claim 11, further comprising circuitry configured to receivesynchronization information, cell identification information, or radionetwork information from the first band.
 15. The mobile station of claim11, further comprising circuitry configured to transmit a first preambleor a second preamble in a ranging or sounding operation, wherein thesecond preamble includes part of the first preamble.
 16. The mobilestation of claim 15, wherein the first and second preambles are OFDMsymbols and the preambles comprise a predetermined sequence or pattern.17. The mobile station of claim 11, further comprising circuitryconfigured to transmit a first preamble or a second preamble in aranging or sounding operation, wherein the second preamble is largerthan the first preamble.
 18. The mobile station of claim 11, furthercomprising circuitry configured to receive a first symbol and a secondsymbol from the first band, wherein the first symbol and the secondsymbol are synchronization information symbols.
 19. The mobile stationof claim 18, wherein the synchronization information symbols are derivedfrom a sequence that has a low cross correlation with other sequencesused for other synchronization information symbols.
 20. The mobilestation of claim 19, wherein the sequence has a low peak to averageratio.
 21. The mobile station of claim 11, wherein the sequence isselected from a plurality of sequences.
 22. The mobile station of claim11, further comprising circuitry configured to receive at least onesymbol from the first band that includes a cell identification of a basestation.
 23. The mobile station of claim 11, wherein the received datachannel is in a time slot format.
 24. The mobile station of claim 11,wherein the OFDMA system operates in an OFDMA frequency division duplex(FDD) or time division duplex (TDD) mode.
 25. A method performed by amobile station, comprising: receiving broadcast information by themobile station to access an orthogonal frequency division multipleaccess (OFDMA) system, wherein the broadcast information is receivedonly in a first band having a first bandwidth and the broadcastinformation is carried by a plurality of groups of subcarriers with eachgroup having a plurality of contiguous subcarriers; determining a secondbandwidth of a second band that is associated with the OFDMA systembased upon the broadcast information received in the first band, whereina second bandwidth of the second band is greater than the firstbandwidth of the first band; and based upon the determination of thesecond bandwidth, receiving the second band, wherein the first band iscontained within the second band, wherein a data channel is carried byat least one subcarrier group of the second band, wherein the pluralityof contiguous subcarriers have fixed spacing, wherein a number of usablesubcarriers is adjustable to realize a variable band, wherein the numberof usable subcarriers is determined based on a plurality of operatingchannel bandwidths, and wherein the first band is defined as a frequencysegment with a bandwidth that is not greater than a smallest operatingchannel bandwidth among the plurality of operating channel bandwidths,the first band having a same value for the plurality of operatingchannel bandwidths, wherein the mobile station is configured to operatewithin the plurality of operating channel bandwidths.
 26. The method ofclaim 25, further comprising receiving a preamble that carriesinformation on sector identity or cell identity.
 27. The method of claim25, further comprising receiving information about the second band toenable the mobile station to receive the data channel.
 28. The method ofclaim 25, further comprising receiving synchronization information, cellidentification information, or radio network information from the firstband.
 29. The method of claim 25, further comprising transmitting afirst preamble or a second preamble in a ranging or sounding operation,wherein the second preamble includes part of the first preamble.
 30. Themethod of claim 29, wherein the first and second preambles are OFDMsymbols and the preambles comprise a predetermined sequence or pattern.31. The method of claim 25, further comprising transmitting a firstpreamble or a second preamble in a ranging or sounding operation,wherein the second preamble is larger than the first preamble.
 32. Themethod of claim 25, further comprising receiving a first symbol andsecond symbol from the first band, wherein the first symbol and thesecond symbol are synchronization information symbols.
 33. The method ofclaim 32, wherein the synchronization information symbol is derived froma sequence that has a low cross correlation with other sequences usedfor other synchronization information symbols.
 34. The method of claim33, wherein the sequence has a low peak to average ratio.
 35. The methodof claim 33, wherein the sequence is selected from a plurality ofsequences.
 36. The method of claim 25, further comprising receiving atleast one symbol from the first band that includes a cell identificationof a base station.
 37. The method of claim 25, wherein the received datachannel is in a time slot format.
 38. The method of claim 25, whereinthe OFDMA system operates in an OFDMA frequency division duplex (FDD) ortime division duplex (TDD) mode.